Polling-Based Focus Detection

[hannesdelbeke]

⚠️ Polling-Based Focus Detection

[!warning] Performance Concern
15 FPS timer constantly polls window state, causing continuous CPU usage even when idle.

Current Issue:

tick = int(1000 / FOCUS_FRAMERATE)  # ~66ms
self.timer.start(tick)

def on_update(self):
    # Runs every 66ms
    if self.blender_focus_toggled():
        bqt.manager._blender_window_change(self._active_window_hwnd)

Problems:

• Continuous CPU usage even when idle
• 66ms latency in focus detection
• Doesn't scale well with many widgets
• Battery drain on laptops

[!tip] Event-Driven Alternative
Use OS-native event hooks instead of polling

Windows:

# Use Win32 message hooks for WM_ACTIVATE
def install_focus_hook():
    WH_CALLWNDPROC = 4
    callback = WINFUNCTYPE(c_long, c_int, c_uint, c_long)

    def hook_proc(nCode, wParam, lParam):
        if msg.message == WM_ACTIVATE:
            on_focus_changed(wParam != WA_INACTIVE)
        return CallNextHookEx(None, nCode, wParam, lParam)

    hook = callback(hook_proc)
    SetWindowsHookEx(WH_CALLWNDPROC, hook, None, GetCurrentThreadId())

macOS:

# Use NSNotificationCenter
from AppKit import NSWorkspace, NSNotificationCenter

def setup_focus_observer():
    nc = NSNotificationCenter.defaultCenter()
    nc.addObserver_selector_name_object_(
        self,
        'applicationDidBecomeActive:',
        'NSApplicationDidBecomeActiveNotification',
        None
    )

Impact: Could reduce idle CPU usage to near-zero.

[hannesdelbeke]

this needs more testing once implemented.
and on both OS
can we keep old solution on mac to split PR in 2 parts?